The present invention relates generally to a semiconductor device and more particularly to a semiconductor device suited for miniaturization.
As one type of semiconductor device, there has been known a circuit structure in which two different types of semiconductor elements are connected in parallel with polarities opposite to each other (i.e. in an anti-parallel connection) and in which a plurality of anti-parallel connections are connected in series to one another. As a typical one of this type of semiconductor device, there can be mentioned an inverter which is composed of gate turn-off thyristors (hereinafter also referred to as GTO in abbreviation). By way of example, reference may be made to Japanese Patent Application Kokai (Laid-Open) No. 9349/1983 (JP-A-58-9349).
As discussed also in the abovementioned publication, one of the most significant requirements imposed on this type of semiconductor device is the cooling of the device. In this conjunction, there have heretofore been made numerous proposals.
The semiconductor device disclosed in the abovementioned patent application is of such a structure in which a combination of two discrete GTOs is provided in each of the anti-parallel connections. In recent years, however, the combination of the two GTOs tends to be replaced by the single GTO with the advent of the gate turnoff thyristor of a large capacity. Increases in the capacity of the GTO is however accompanied with corresponding increases in the amount of heat generated by one GTO element, which in turn means that the cooling of the GTO device presents a more serious problem to be solved.
FIG. 1 of the accompanying drawings shows in a wiring diagram a general arrangement of a three-phase inverter in which each of the anti-parallel connections includes a single GTO. In each phase of this inverter circuit, e.g. in U-phase 16, a GTO 21 is connected in anti-parallel with a diode 31 to constitute an anti-parallel connection, which in turn is connected in series to another anti-parallel connection of a GTO 22 and a diode 32. Also in V-phase 17 and W-phase 18, identical circuit configurations are adopted, wherein all phase conductors are connected to a load such as an electric motor 19. In FIG. 1, a reference numeral 1 denotes a capacitor, 4 denotes a reactor, 5 denotes a diode and numerals 12 and 13 denote input terminals connected to a power supply source (not shown).
Now, considering the order of stacking the semiconductor elements 5, 21, 22, 31 and 32 which belongs to one phase, e.g. U-phase, they are connected electrically in such a manner as illustrated in FIG. 2 of the accompanying drawings. Further, these semiconductor elements are physically integrated in such a cooling structure as shown in FIG. 3, which is a typical one of the cooling structures known heretofore and so implemented as to cool the semiconductor elements by making use of vaporization of a cooling medium or coolant under heat generated by the semiconductor elements. For more particulars of the cooling structure known heretofore, reference may be made, for example, to Japanese Patent Application Kokai (Laid-Open) No. 123277/1975 (JP-A-50-123277).
Referring to FIG. 3, reference numerals 61 to 65 denote cooling fin members, respectively, each of which accommodates therein a coolant susceptible to boil at a relatively low temperature such as Fron (Freon) so that the coolant is vaporized under the heat generated by the adjacent semiconductor elements to thereby deprive the latter of heat. The resulting vapor is introduced into a condenser 9 through insulated tubes 81 to 85 to undergo heat-exchange with the ambient atmosphere.
In the cooling structure shown in FIG. 3, each of the fins 61 to 65 is heated by the adjacent semiconductor elements located on both sides. Consequently, each fin is required to exhibit a sufficiently high cooling capability in order to cool both of the associated semiconductor elements. In the past, this was accomplished only by increasing the size of the cooling fin. However, in the case of an inverter destined for controlling a drive motor for an electric car mounted underneath the car floor, severe restriction is imposed on the size of the device. In other words, a limit is encountered in increasing the size of the cooling fin. Under the circumstance, there exists a great demand for improving the structure of the semiconductor device such as the inverter inclusive of the cooling system so that the size of the device can be reduced.